Method for Control of a Drilling Operation

ABSTRACT

A method for controlling a drilling operation, in particular in production or exploration drilling for hydrocarbons, in which a drill bit is arranged on an end of a drill string and, by rotation and pressure against an underground formation, is arranged to form a borehole, and in which a drilling fluid is circulated through a pipe bore into the borehole at the drill bit to convey cuttings out of the borehole. The method comprises the steps of: providing data on the particle size distribution of the cuttings; comparing the provided particle size distribution with data for the desired particle size distribution when drilling in the underground formation of interest; and adjusting the critical control parameters of the drilling operation with the aim of achieving a cuttings particle size distribution which corresponds, to the greatest extent possible, to the desired particle size distribution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the US National Phase application of PCT Application No. NO20009/000006 filed 7 Jan. 2009, which claims priority to Norwegian Application No. 20080204.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable

REFERENCE TO A SEQUENCE LISTING

Not Applicable

BACKGROUND OF THE INVENTION

The invention relates to a method for controlling a drilling operation, more particularly by the particle size distribution of cuttings being determined and compared with data for the desired particle size distribution when drilling the underground formation of interest, after which the critical control parameters of the drilling operation are changed with the aim of achieving the desired particle size distribution in the cuttings.

In connection with the drilling of exploration or production wells for hydrocarbons, among other things, the drilling fluid used is cleaned of drilled particles (cuttings) which have been carried hydraulically with the drilling fluid from the bottom of the borehole up to the surface. The drilled particles must be separated from the drilling fluid for the properties of the drilling fluid to be recovered. In connection with boreholes in underground formations chemicals and minerals are also added to seal the wall of the borehole, among other things, to prevent, thereby, drilling fluid from leaking out through the borehole wall to the formation.

In connection with drilling long, horizontal holes it is a problem that particles carried in the drilling fluid tend to sediment in the borehole, as they are deposited substantially in the bottom portion of the horizontal borehole. This leads to a decreasing cross-section of the borehole, resulting in increasing contact between the drill pipes of a drill string and the sedimented mass. This gives increased friction during movement of the drill string, and more power is needed to move the drill string. At worst the drill string gets stuck in the borehole. This problem grows with increasing borehole lengths.

From the mining industry, for example, it is known to get an overview of the particle size distribution of a particle mass by a selection (sample) of the particle mass being screened by means of a screening apparatus comprising a plurality of screen cloths decreasing in mesh width downstream, the different fractions being collected and weighed, after which the relative distribution is arranged in a table or diagram. An example of this is described in EP0084666.

In the recovery of drilling fluid in connection with exploration or production drilling for hydrocarbons, it is known to use one or more shale shakers, each of the shale shakers can be provided with screen cloths of different apertures assembled into a screen assembly. Each screen cloth delivers the separated particles to the same place, the purpose of using several screen cloths being to achieve a best possible separation of particles from the drilling fluid. The separated particles are handled as gravel in the subsequent process.

From EP 84666 B1, US 2007/245838 A1, U.S. Pat. No. 6,386,026 B1 and U.S. Pat. No. 3,943,754 are known devices and methods for determining the particle size distribution of cuttings from return drilling fluid. Besides, from the U.S. Pat. No. 6,386,026 B1 and also NO 3186532 B1, U.S. Pat. No. 7,092,822 B2 and U.S. Pat. No. 6,349,595 B1 it is known to analyse cuttings particles for interpreting different petrophysical or chemical parameters such as formation permeability, capillary pressure, rate of penetration, recirculation rate for drilling mud etc.

BRIEF SUMMARY OF THE INVENTION

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art.

The invention relates to a method for controlling a drilling operation, in which a drill bit is arranged in a manner known per se on an outer end of a drill string, and a drilling fluid, which is circulated in the borehole, carries cuttings out of the borehole. By finding the particle size distribution of the drilling fluid and comparing this particle size distribution with an ideal desired distribution when drilling under the prevailing conditions, the analytical result may be used for controlling the drilling operation, more particularly, in the event of the analytical results showing a fraction distribution which is not favourable, by seeking to change the drilling operation into a direction towards a more favourable result. The control parameters that affect the particle distribution in a given underground structure are, for example, the work pressure of the drill bit against the underground formation, the rotational speed of the drill bit, the composition of the drilling fluid and the flow rate of the drilling fluid in the borehole. It is obvious to a person skilled in the art that any method of separation suitable for separating cuttings particles from a drilling fluid will be appropriate as long as the separating method enables fractioning of the cuttings particles.

More specifically, the invention relates to a method for controlling a drilling operation, in particular in the production or exploration drilling for hydrocarbons, in which a drill bit is arranged on an end of a drill string and, by rotation and pressure against an underground formation, is fit to form a borehole, and in which a drilling fluid is circulated through a pipe bore into the borehole at the drill bit to convey cuttings out of the borehole, characterized by the method comprising the steps of: providing data on the particle size distribution of the cuttings; comparing the provided particle size distribution with data for the desired particle size distribution when drilling in the underground formation of interest; and adjusting the critical control parameters of the drilling operation with the aim of achieving a cuttings particle size distribution which corresponds, to the greatest extent possible, to the desired particle size distribution.

The critical control parameters of the drilling operation may comprise the work pressure of the drill bit against the underground formation, the rotational speed of the drill bit, the composition of the drilling fluid and the flow rate of the drilling fluid in the borehole.

The cuttings particle size distribution may be provided by at least a representative portion of the cutting-laden drilling fluid being carried to a separating system arranged for fractioning the cuttings particles. Thereby the advantage is achieved that the method according to the invention may be used in the analysis of representative samples from a flow of drilling fluid from a borehole. Alternatively, the entire flow of drilling fluid can be treated, which is advantageous when there is a need for special processing of one or more cuttings fractions.

The separating system may comprise a plurality of shale shakers connected in series, each shale shaker being arranged to separate particles over a specific screening size and keep them separated from particles which are separated from other shale shakers in the screening device. The method may thereby be practised with the use of shale shakers known per se but arranged in such a way that the separated particles from one screen size do not get mixed with fractions separated from shale shakers of a different screen aperture.

Each fraction may be quantified in the form of weight or volume. It is obvious that there is a wide variety of measuring methods for finding the relevant measuring quantities. Each of the separate particle fractions can be distributed for further processing. By processing is meant here any use of the cuttings, for example disposal, crushing or direct return to an underground structure.

BRIEF DESCRIPTION OF THE DRAWING

In what follows is described an example of a preferred embodiment which is visualized in the accompanying drawing, FIG. 1, which shows schematically an array of multiple shale shakers for practising the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the FIGURE is shown a separating system 1, in which several first shale shakers 11, of the prior art known per se, have been arranged around a first screening receiver 12. All the first shale shakers 11 are provided with the same type of screen cloth (not shown) for separating a first cuttings fraction A of a partial material flow 16 which is carried via the first screening receiver 12, which is shared by all the first shale shakers 11, to a first conveyor 13. The first conveyor 13 is provided with means 18 for registering the material flow passing over said conveyor 13. From the outlet of the first conveyor 13 flows a material flow 17 containing separated cuttings of the fraction A. This material flow 17 may be split, as required, into several material flows 17 a, 17 b for different further processing; for example, one partial flow may be a material flow which is used for sampling according to the invention, whereas the other partial flow may be carried to a landfill (not shown) directly or via conveyor means, known per se, suitable for this.

Each of the first shale shakers 11 is supplied with cuttings-laden drilling fluid in a primary drilling fluid flow 5 in a manner known per se. For simplicity, the supply of drilling fluid to only one of the shale shakers 11 is shown.

In a fluid outlet from each of the first shale shakers 11 flows a secondary drilling fluid flow 15. For simplicity, this is shown in connection with only one of the shale shakers 11. The secondary drilling fluid flow 15 is carried to an inlet of a second shale shaker 21.

In a manner corresponding to that described above for the first shale shakers 11, several second, respectively third and fourth, shale shakers 21, respectively 31 and 41, of the prior art known per se, are placed together around a second, respectively third and fourth screening receiver 22, respectively 32 and 42.

All the second shale shakers 21 are provided with a screen cloth (not shown) with smaller apertures than the screen cloth of the first shale shakers 11 for separating a second cuttings fraction B of a partial material flow 26 which is carried via the second screening receiver 22 which is shared by all the second shale shakers 21 to a second conveyor 23.

Corresponding conditions apply to the third and fourth shale shakers 31, 41 separating a cuttings fraction C, respectively D.

The second conveyor 23, respectively the third and fourth conveyors 33 and 43, is provided with means 28, respectively 38 and 48, for registering the material flow passing over said conveyor 23, respectively 33 and 43. From the outlet of the second conveyor 23, respectively the third and fourth conveyors 33 and 43, flows a material flow 27, respectively 37 and 47, containing separated cuttings of the fraction B, respectively C and D. This material flow 27, respectively 37 and 47, may be split, as required, into several material flows 27 a, 27 b, respectively 37 a, 37 b and 47 a, 47 b, for different further processing; for example, one partial flow may be a material flow which is used for sampling according to the invention, whereas the other partial flow may be carried to a landfill (not shown) directly or via conveyor means, known per se, suitable for this.

From the fourth shale shakers 41 runs a flow 45 formed by drilling fluid which is fully processed, as far as the separation of cuttings particles is concerned, but which may undergo further processing, in a manner known per se, for the separation of additives, for example weight materials like barite and similar.

It is obvious to a person skilled in the art that the separating system 1 for practising the method according to the invention must include appropriate prior art pipe, valve, pump and container arrangements, known per se, for controlling the fluid flows in the separating system 1, but which are not shown here for the sake of simplicity.

It is also obvious that the fluid flows 15, 25, 35 are not necessarily carried directly between the respective shale shakers 11, 21, 31, 41 but could be carried via, for example, buffer reservoirs or fluid dispersals (not shown).

It is also obvious that the separating system 1 may include more shale shakers with further types of screen cloth for splitting the cuttings into more, suitable fractions than those mentioned here.

To the separating system 1 are connected, via signal-communicating means 2 a, 3 a known per se, for example cables, control and operation plants 2, 3 for controlling the separating system 1 and for recording and calculating relevant data.

While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claims, including the full range of equivalency to which each element thereof is entitled. 

1. A method for controlling a drilling operation, in production or exploration drilling for hydrocarbons, in which a drill bit is arranged on an end of a drill string and, by rotation and pressure against an underground formation, is arranged to form a borehole, and in which a drilling fluid is circulated through a pipe bore into the borehole at the drill bit to convey cuttings out of the borehole, the method comprising the steps of: providing data (17, 27, 37, 47) on the particle size distribution of the cuttings; comparing the provided particle size distribution with data for a targeted particle size distribution when drilling in the underground formation of interest; and adjusting the critical control parameters of the drilling operation with the aim of achieving a cuttings particle size distribution which corresponds, to the greatest extent possible, to the targeted particle size distribution; the critical control parameters of the drilling operation including the work pressure of the drill bit against the underground formation, the rotational speed of the drill bit, the composition of the drilling fluid, and the flow rate of the drilling fluid in the borehole.
 2. The method in accordance with claim 1, wherein the cuttings particle size distribution is provided by at least a representative portion of the cuttings-laden drilling fluid being carried to a separating system (1) arranged to fraction the cuttings particles.
 3. The method in accordance with claim 2, further including a separating system (1) having a plurality of shale shakers (11, 21, 31, 41) connected in series, each shale shaker (11, 21, 31, 41) being arranged to separate a fraction (A, B, C, D) of particles over a specific screening size and keep each fraction (A, B, C, D) separated from the fractions (A, B, C, D) separated from other shale shakers (11, 21, 31, 41) in the separating system (1).
 4. The method in accordance with claim 2, wherein each fraction (A, B, C, D) is quantified in the form of weight or volume.
 5. The method in accordance with claim 3, wherein each of the separate particle fractions (A, B, C, D) is distributed to further processing. 